1. Field of the Invention
The present invention relates to a method of brazing a metal work, or in particular to a method of brazing a metal work effectively applicable to a heat exchanger of aluminum such as a radiator.
2. Description of the Related Art
As a method of brazing the heat exchanger, Japanese Unexamined Patent Publication No. 7-185796, for example, discloses an invention in which a work such as cooling fins is immersed in a suspension constituted of a flux and an aqueous solution of a binder formed of resin, the suspension is coated on the work, and the work is dried by being heated to attach the flux securely on the work surface, after which the work is brazed by being heated in a furnace.
In the invention disclosed in the aforementioned patent publication, however, the suspension of the aqueous solution of the binder and the flux is simply coated on the work. In the case where the suspension is coated while foreign matters such as a metal piece or the like are attached to the surface of the work, vibration or rubbing against other works during transportation of the work may separate the foreign matter from the surface of the work before it is dried by being heated, with the probable result that the flux attached to the surface of the foreign matter will come off with the foreign matter.
Also, in the case where oil such as a coolant becomes attached to the surface of the work, the flux is repelled along with the water in the suspension. In actual practice, therefore, the flux substantially cannot be coated on a portion to which oil is attached.
To cope with these problems, foreign matter and oil attached to the surface of the work are desirably removed by washing the work sufficiently. This, however, increases number of steps (time) for washing the work, resulting in an increased number of production steps for the heat exchanger, leading to increased production cost.
In view of the above problem, the object of present invention is to ensure that the flux is securely coated (attached) on the surface of the work.
In order to achieve the object described above, according to a first aspect of this invention, there is provided a method of brazing a metal work, comprising the steps of heating the metal work to at least the softening temperature of resin, coating a flux mixed with a binder of resin on the work, drying the work coated with the flux, and brazing by heating the work.
As a result, the binder attached to the surface of the work is softened for increased stickiness. Even if foreign matter becomes attached to the surface of the work, therefore, the binder causes the flux, together with the foreign matter, to attach to (couple with) the work surface securely. Thus, the flux can be securely coated (attached to) on the work surface.
As described above, according to this invention, the flux can be coated (attached) securely on the work surface without increasing the number of steps (time) for washing the work, or without the washing process.
According to a second aspect of the invention, there is provided a method of brazing a metal work, comprising the steps of heating the metal work to at least the softening temperature of resin and not lower than water evaporation temperature, coating the work with a suspension constituted of the flux and an aqueous solution of a binder formed of resin, drying by heating the work coated with the flux, drying the work coated with the flux, and brazing by heating the work.
As a result, the binder attached to the work surface is softened and increases in stickiness. Even if foreign matter become attached to the work surface, therefore, the binder causes the flux together with the foreign matter to attach firmly on the work surface. Thus, the flux can be securely coated (attached) on the work surface.
Also, in view of the fact that the temperature of the work is not lower than the evaporation temperature of water, even if oil becomes attached to the work surface, water in the suspension is evaporated before it can be repelled by the oil, and thus the flux is prevented from being repelled together with the water.
As described above, according to this invention, the flux can be coated (attached) securely on the work surface without increasing the number of steps (time) for washing the work, or without the washing process.
According to a third aspect of the invention, there is provided a method of brazing a metal work in which the binder is desirably made of acrylic resin in the case where the work is made of an aluminum alloy.
According to a fourth aspect of the invention, there is provided a method of brazing a metal work in which the binder is desirably made of 3-methoxy-3-methyl-1-butanol in the case where the work is made of an aluminum alloy.
According to a fifth aspect of the invention, there is provided a method of brazing a metal work in which the binder is desirably made of N,N-dimethyl aminoethanol in the case where the work is made of an aluminum alloy.
Incidentally, the above words in parenthesese are indicative of an example of the relation with corresponding specific means described later in embodiments.